We propose to conduct a telephone survey of a national probability sample of 3,500 U.S. men and women aged 50-75 years that will describe the prevalence of high risk behaviors within this age group. Ten percent of AIDS cases are among persons aged 50 and older. Unfortunately, no reliable estimates exist of the risk for further HIV transmission within this age group. Needed is a more complete understanding of the sexual practices of older Americans and valid estimates of the proportion of older Americans with a history of blood-transfusions, intravenous drug use, or high-risk male homosexual behaviors. First, we will measure the point prevalence of specific behaviors related to HIV transmission and prevalence since 1977 of blood transfusions among older Americans. Prevalence estimates will also be generated separately for AIDS epicenters and for the combined geographical areas that lie outside of the major American centers of the epidemic. Second, using the three-stage AIDS Risk Reduction Model (Catania, Kegeles and Coates, in press), we will identify the determinants of behaviors implicated in the spread of HIV infection among older Americans. Data from this project will provide needed information regarding the prevalence and determinants of high risk behaviors for HIV transmission among Americans over the age of 50, a subset of the population that has heretofore been neglected in AIDS prevention research. By measuring absolute levels of risk and by identifying the determinants of risk for HIV transmission within this population, our ability to design effective AIDS prevention campaigns for older Americans will be qualitatively improved.